In the related art, as one of systems which purify exhaust gas of an automobile, there has been known a selective catalytic reduction (SCR) system that reduces NOx to nitrogen and water using ammonia, and zeolite having a copper-carried CHA structure is paid attention as zeolite achieving SCR catalysis.
In this SCR system, a honeycomb unit, in which a large number of through holes allowing the exhaust gas to pass therethrough are arranged in parallel to extend in a longitudinal direction, is used as an SCR catalyst carrier. For example, as one that aims to enhance heat resistance and endurance in a case of being used as an SCR catalyst carrier, zeolite having a CHA structure is disclosed in Patent Literature 1 in which a composition ratio of SiO2/Al2O3 is less than 15 and a particle size is 1.0 to 8.0 μm.
On the other hand, a method for producing zeolite having a CHA structure in which Cu is carried is disclosed in, for example, Patent Literature 2 in which the zeolite having the CHA structure having a molar ratio of silica to alumina more than 10 is subjected to ion exchanged using copper acetate having a concentration of about 0.001 to 0.25 mol and/or an ammoniacal solution of copper ions.